Polyester hairbrush bristle

ABSTRACT

Monofilament brush bristle prepared from a blend of polyethylene terephthalate exhibits improved bend recovery characteristics.

BACKGROUND OF THE INVENTION

In the development of synthetic filaments for the replacement of hogbristles in hair brushes, a wide variety of polymers has been explored.While oriented nylon monofilaments have been used most frequently inthis application, effort has been directed toward the use of variouspolyesters in brush bristles to take advantage of the properties ofthese materials. An important characteristic for brush bristles is theability of the bristles to retain their original shape with extendeduse. Typically, this retention of shape is designated as Mandrel BendRecovery (MBR), that is, the extent to which a monofilament will recoverits original configuration after being bent over a mandrel. In addition,of course, a brush bristle must exhibit satisfactory tensile strengthfor normal usage and good dimensional stability when exposed to elevatedtemperatures. Continuing effort has been directed toward the idealbalance of these properties for polyester filaments.

SUMMARY OF THE INVENTION

The instant invention provides a polyester hairbrush bristle thatprovides an excellent balance of properties and particularly goodMandrel Bend Recovery characteristics.

Specifically, the present invention provides a monofilament suitable foruse as a hairbrush bristle having a diameter of about 5-10 mils andwhich is oriented about 3-5 times in the longitudinal direction, thepolymeric components of the monofilament consisting essentially of,complementally, about 65-75 weight percent polybutylene terephthalateand about 35-25 weight percent polyethylene terephthalate, and whereinthe monofilament exhibits a Mandrel Bend Recovery after ten cycles of atleast about 80%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are graphical representations of the Mandrel Bend Recoverycharacteristics of blends of polybutylene terephthalate and polyethyleneterephthalate for one and ten Mandrel Bend Recovery cycles,respectively.

DETAILED DESCRIPTION OF THE INVENTION

The polymers used for the preparation of the present hairbrush bristlesare polyethylene terephthalate and poly(1,4-butylene terephthalate).These polymers are well known as film and fiber forming materials andcan be prepared by the method described in Whinfield et al. U.S. Pat.No. 2,465,319, hereby incorporated by reference. The polymers are alsocommercially available from a wide variety of sources.

In accordance with the present invention, the polyethylene terephthalateand polybutylene terephthalate are melt blended to provide,complementally, about 60-80% polybutylene terephthalate and about 40-20%weight percent polyethylene terephthalate. Blends having about 65-75weight percent polybutylene terephthalate and about 35-25 weight percentpolyethylene terephthalate provide still superior Mandrel Bend Recoverycharacteristics, and blends of about 70% polybutylene terephthalate andabout 30% polyethylene terephthalate are particularly preferred. Thepolymers can be blended using any apparatus that will provide asubstantially uniform mixture of the two components. Separate blendingapparatus, such as a Banbury mixer, can be used prior to extrusion, orthe polymeric components can be blended in the extrusion apparatus usedfor the preparation of the monofilament.

The polyethylene terephthalate and polybutylene terephthalate, in theindicated ratios, make up the whole of the polymeric components used inthe present brush filaments, with the exception of minor percentages ofother polymer components which do not substantially effect the overallcharacter of the present polymer blends. However, in addition to thesetwo polymeric components, the present filaments can contain minorquantities, for example, up to about 5 weight percent, of conventionalcolorants, antioxidants or processing aids such as those normally addedto polymeric compositions to facilitate extrusion, as will be evident tothose skilled in the art.

After blending these components, the present monofilaments are treatedin the usual manner and oriented by stretching to improve tensileproperties. Typically, the monofilaments are oriented by stretchingabout 3-5 times their original length at elevated temperatures. Theorientation temperature should be above the glass transition temperatureof the polyethylene terephthalate, and typically about 80°-90° C. Themonofilaments are subsequently set at a temperature of about 150°-180°C., and preferably about 170° C., for a period sufficient to bring thefilament to the heat setting temperature, e.g., about one minute.

The present monofilaments exhibit excellent performance characteristicsas brush bristles. The oriented monofilaments show satisfactory TensileStrength as measured by ASTM test D-638-68, combined with excellentDimensional Stability in boiling water as measured by ASTM testD-124-54. Most importantly, the monofilaments exhibit Mandrel BendRecovery that is noticeably better than that shown by filaments preparedfrom either of the two components of the polymer blend or from ratios ofthe two polymers outside of those specified in the present claims.

The present invention is further illustrated by the following specificexamples, in which parts and percentages are by weight unless otherwiseindicated. In these examples, Mandrel Bend Recovery is measuredaccording to the following procedure:

1. Condition monofilament samples at 23±1.1° C. and 50±2% RH for 48hours.

2. Measure the monofilament diameter to the nearest mil.

3. Attach to one end of the monofilament a weight in grams approximatelyequivalent to 0.5 x (diameter in mils)².

4. Insert the other end in a hole drilled in a 3/32" mandrel. Allow themonofilament and the weight to hang freely in the support.

5. Wrap 10 or more loops around the mandrel, cut off the weight, andfasten the loose end in another hole in the mandrel. Note the number ofloops. Allow to stand for 4 minutes.

6. Cut the monofilment off the mandrel, place in water at 23±1.1° C.,and allow to relax for 1±0.1 hour. Note the number of loops afterrecovery and estimate fractions of a loop to the nearest 1/10 loop.

7. Calculate Mandrel Bend Recovery according to the formula: ##EQU1##

EXAMPLES 1-3 AND COMPARATIVE EXAMPLES A-C

Monofilaments were prepared from polyethylene terephthalate having aninherent viscosity of 0.72, polybutylene terephthalate having aninherent viscosity of 1.08 and commercially available from GeneralElectric Company as "Valox 310", and blends of these two polymers. Thepolymers were first dry blended. The pellets were dried overnight in a110° C. vacuum oven. The blend was then transferred to the hopper of asingle-screw extruder under a nitrogen purge to maintain a dryatmosphere. Filaments were extruded with the extruder operating at atemperature ranging from 266° to 273° C. and a die temperature of 270°C. Billets were then drawn in a single-stage draw unit. The drawapparatus consisted of a pair of takeoff rolls, a pair of fast rolls,and a hot water bath. The polymers or blends, after extrusion, weredrawn four times by running the fast rolls of the draw apparatus fourtimes faster than the takeoff rolls. After orientation, the drawnfilaments were heat set in a 170° C. oven for 1 minute. The orientedfilament diameter was 10 mils.

The filaments were evaluated according to the test procedures describedabove for Mandrel Bend Recovery, Tensile Strength and DimensionalStability. The results are summarized in the following Table andgraphically represented in the FIGS. 1 and 2 for one and ten MandrelBend Recovery cycles, respectively.

                  TABLE                                                           ______________________________________                                                                                 Dimen-                                                                 Tensile                                                                              sional                               Exam- Blend     MBR     MBR Values                                                                              Strength,                                                                            Stabil-                              ple   Comp.     Cycle   @ 5% Relax, %                                                                           Kpsi   ity %                                ______________________________________                                        A     4GT       1       82        43     1.89                                                 10      78                                                    1     80% 4GT   1       86        40     2.33                                       20% 2GT   10      81                                                    2     70% 4GT   1       90        31     .26                                        30% 2GT   10      83                                                    3     60% 4GT   1       82        41     .69                                        40% 2GT   10      73                                                    B     50% 4GT   1       77        38     .72                                        50% 2GT   10      62                                                    C     2GT       1       72        58     .50                                                  10      53                                                    ______________________________________                                    

I claim:
 1. A monofilament suitable for use as a brush bristle having adiameter of about 5-10 mils and being oriented about 3.0-5.0 times in alongitudinal direction, the polymeric components of the monofilamentconsisting essentially of, complementally, about 65-75 weight percentpolybutylene terephthalate and about 35-25 weight percent polyethyleneterephthalate, and wherein the monofilament exhibits a Mandrel BendRecovery after ten cycles of at least about 80%.
 2. A brush bristle ofclaim 1 consisting essentially of about 70 weight percent polybutyleneterephthalate and about 30 weight percent polyethylene terephthalate.